The present invention relates to acetylene black, particularly acetylene black useful for obtaining granular acetylene black excellent in dispersibility in rubber, plastic, etc. and conductivity-endowing effect and low in dust scattering, to granular acetylene black made from the acetylene black, and to a method of making same.
Acetylene black has a partly-graphitized structure, and its properties are intermediate between those of graphite and amorphous carbon. Its particles form a steric chain structure (hereinafter called structure). Hence, it is excellent in conductivity, liquid absorbing ability, compressibility and elasticity. Also, it is carbon black of high carbon purity, which has few factors for contamination with impurities. Therefore, it is praised for its use, for example, as an additive to rubber, plastic, etc. (hereinafter solely called plastics) as a pigment, conductivity-endowing agent or the like.
The acetylene black, like other carbon blacks, is too difficult to treat in an intact state after production, and has a very small bulk specific gravity. The result of this is that transport of the material is difficult and its dust scattering is remarkable. In addition, users require that the treatment of it in bulk form be easy. Accordingly, under the existing circumstances, powdered acetylene black is granulated before use. The desirable properties of the resultant granulated acetylene black are described in "Instructions in Experimental Methods on Carbon Black for Rubber (JIS K 6221). Namely, the granulated acetylene black is required to be excellent in fluidity, difficult to be damaged and hard to scatter from the standpoint of the treatment. On the other hand, when used as an additive to plastics, it is required to be composed of soft particles which disperse readily.
The conventional granular acetylene black, however, has possessed the following disadvantage. It has given rise to a decrease in strength of plastics and a lack of smoothness of the plastic surface due to the poor dispersibility, whereby the functions inherent in the plastic have been greatly deteriorated.
In order to overcome the above drawback, the dispersibility has been raised by endowing the granular acetylene black with a strong shearing force using a processing machine, such as an extruder, injection molding machine or the like, excellent in dispersing ability. However, the strong shearing force given to the granular acetylene black has destroyed the structure of it, whereby the characteristics of the acetylene black have not satisfactorily been demonstrated. It has been also the cause for the deterioration of the functions inherent in the plastic. Furthermore, since the conventional granular acetylene black has possessed an original structure insufficient in strength, the above-described strong shearing force has undesirably promoted further destruction of the structure.
Hence, it has been desired that a plastic additive be provided comprising acetylene black having a strong structure and no dust scattering and being excellent in dispersibility.